Pipettes are widely used in many laboratory procedures. When pipettes are used in a serological laboratory, there is often a need to make sterile fluid transfers and the pipettes used are sterilized. In response to this need, several manufacturers produce disposable plastic serological pipettes in a variety of maximum capacities, e.g., 1, 2, 5, 10, 25, 50 and 100 milliliters (ml), etc., with intermediate volume scale markings in tenths, halves or other unit ml increments. The American Society for Testing and Materials (ASTM) describes the structure and marking of these pipettes in detail in ASTM Standard No. E 934-85. In order to facilitate handling the pipet and to avoid drawing fluid out of the pipet during filling, there is generally a space on the barrel between the end of the scale and the neck of the pipet. A pipet following the ASTM Standard No. E 934-85 has a minimum of 90 mm between the end of the scale and the top of the pipet.
Previously, it was common for the operator to apply suction to the pipet for drawing fluid into the pipet by placing the neck of the pipet in his mouth. The neck portion often still is referred to as the "mouthpiece." As a convenience, these pipettes are commercially available in sterile form and individual peel-open packages that maintain the sterility of the pipet contained until the package is opened. Most of these packages are formed from paper, nonwoven materials and plastic film. Most of these packaging materials are either opaque or translucent and it is generally not possible to read the scale on the pipet through the package.
Because of the well documented concerns about laboratory safety in oral pipetting, most laboratory protocols now prohibit oral pipetting and require the use of suction bulbs or mechanical pipetters. Thus, in many normal procedures, it is common to use these sterile pipettes with a mechanical pipetter, to draw and expel the fluids being handled. In these laboratory sterile protocols and practices, the operator opens only the top portion of the sterile package, exposes only the neck of the pipet and mounts the pipet into a holder on the pipetter using the wrapper to grasp the pipet. The operator only removes the balance of the of the package when ready to perform the fluid transfer.
Most commercially available pipettes have volume indicating markings that are best read from a particular angle. Thus, if the pipet is not mounted in the pipetter so that the markings are positioned to be easily read by the operator, the operator must either make the reading in a less than optimal position, increasing the possibility of reading error, or grasp the now uncovered pipet and rotate it within the holder to the optimal reading position. By grasping the uncovered pipet and rotating it, there is a distinct possibility that the pipet may be contaminated with microorganisms.
If a pipet had an indication of the radial orientation of the scale at the top portion, the operator could optimally place the pipet in the pipetter before complete removal of the package and eliminate a possible source of misreading or contamination. Such a pipet is described below.